Depositing a coating on various parts is known, as are materials for various decorative or functional applications. The known methods for such depositions are typically chemical vapour deposition (CVD), physical vapour deposition (PVD) or electrodeposition for example.
However, these methods have the drawback of creating inhomogeneous thicknesses in the case of certain complex geometries, such as for example concave geometries. This may, for example, result in surface smoothing in the case of a surface known as “clous de Paris” within the field of horology.
Moreover, these methods have the drawback of not allowing much flexibility in the choice of pairs of substrate-layer materials. In fact, in practice, it is not possible to deposit any type of layer on any type of material with large thicknesses. This is due to various factors such as thermal stresses or the incompatible crystallographic structure of the substrate material and the material of the layer or other elements.
A method for depositing a diamond coating is also known which partly overcomes these drawbacks. This method, known from FR Patent No. 2 815 045, includes the following steps:
1) Forming the negative form of the part which it is desired to make, from silicon.
2) Depositing a 2 μm diamond layer on the negative by chemical vapour deposition (CVD).
3) Overmoulding the negative using an epoxy resin.
4) Selectively dissolving the negative with hydrofluoric acid without dissolving the epoxy resin or the diamond layer.
The drawback of this method is that it cannot be used for plastics or polymers or for crystalline metals. Indeed, the use of crystalline metal for this coating deposition method is not possible for several reasons.
First of all, metals do not generally have the adherence properties that a resin or plastic material may have. Indeed, epoxy is a polymer which, when it polymerises, has the properties of an adhesive with a good traction factor with materials such as wood, metal, glass, etc. Consequently, since metals have low adhesion properties, the application of the method disclosed in FR Patent No. 2 815 045 to a crystalline metal will not allow for deposition of a layer which will adhere to the part to be made.
Secondly, some characteristics of metals may prevent the use thereof in the method disclosed in the prior art. Thus, in general, for the metals to be able to be shaped in a mould, they must be placed in liquid form, i.e. melted. A certain number of metals have a melting temperature of more than 1000° C. Consequently, this type of melting temperature can damage the layer deposited on the negative, particularly if said layer is thin, or even damage the negative itself.
In addition to other characteristics which may discourage those skilled in the art from using metals in the method disclosed in the prior art, solidification shrinkage or the difference between the expansion coefficients of the layer and metal may be cited. Solidification shrinkage consists in a contraction of the metal on itself during solidification. This then leads to an approximately 5 to 7% reduction in the dimensions of the solid part compared to the dimensions of the negative. There is therefore a risk of delamination between the layer and solidified metal. This risk of delamination may also be caused by the difference between the expansion coefficients of the layer and the metal, the expansion coefficient of the metal being generally much larger than that of the layer.
Therefore, it is reasonable to assume that those skilled in the art would not have used the method disclosed in FR Patent No 2 815 045 to manufacture a metal part coated with a layer.